Many devices, such as light-emitting diode drivers and battery chargers use flyback converters as current sources. A flyback converter converts an input voltage to a constant current source using a transformer. By controlling the current flow in the primary side of the transformer (sometimes referred to as primary current), the output current is regulated. A switch controlled by a controller and connected to the primary side of the transformer controls the primary current. The controller may use pulse width modulation (PWM) to control the on time and off time of the switch.
In new applications, greater current regulation is required, which requires greater control of the switching time. One limitation in the control of the primary current is the propagation delay when the controller turns the switch off. The propagation delay may cause the switch to stay on longer than it was intended, which causes greater peak current on the primary side of the transformer. Moreover, the additional value of the peak current is also dependent on the line voltage and the primary inductance value of the transformer. In summary, the output current is greater than intended and it is dependent on other parameters that are not fully under control.